Aqueous spin bath



United States Patent 3,034,414 AQUEGUS SHN BATH John W. Soehngen, Berkeley Heights, N.J., Stewart W.

Morse, Jr., Media, Pa, and Cipriano Cipriani, Merrie town, NJ, assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed June 17, 1959, Ser. No. 820,365

10 Claims. (Cl. 28-82) This invention relates to the spinning of cellulose triacetate to form filamentary materials.

In application Serial No. 730,021 filed April 21, 1958 by Jesse L. Riley (the disclosure of which is hereby incorporated herein by reference) there is disclosed a process for the wet spinning of cellulose triacetate from its solution in a solvent comprising methylene chloride into a non-solvent bath, hereinafter termed a spin-bath, containing methylene chloride and a lower aliphatic alcohol, preferably methanol. The resulting filamentary material is stretched in the spin bath and the product is characterized by high tenacity and elongation. It is disclosed that for any given set of spinning conditions, there is a certain ratio of methylene chloride to the alcohol in the spin bath at which the tensile strength and elongation at break of the resulting filamentary material are both at their optimum values. That is, when curves are drawn relating tenacity and elongation, respectively, to the concentration of methylene chloride in the spin bath, all other factors being the same, both curves reach their maximum values at about the same concentration of the methylene chloride. The concentration of methylene chloride varies from about 25 to 65% of the total weight of methylene chloride plus alcohol. The temperature of the spin bath generally ranges from about 15 to 45 C., though when operating at atmospheric pressure it is preferable to use a temperature below 40 C. to' avoid formation of bubbles of solvent. The weight percent concentration of methylene chloride in the spin bath on an anhydrous basis, C, is approximately related to the spin bath temperature in degrees centigrade, T, by the equation C=75 AT-' -5. Desirably the extruded filaments are stretched as formed, by being taken up at a higher linear speed than the linear speed at which they are extruded. The ratio of these two speeds is known as the draw-down ratio. A suitable range of draw-down ratios is about 15:1 to 35:1, preferably 10:1 to :1. The actual speed of take up in the process may be quite high, for example in excess of 75 meters per minute.

The filamentary materials so prepared have tenacities of over 1.8, e.g. 2 or higher, grams per denier accompanied by elongations of over 18%, e.g. 20% or higher, even for filaments whose denier is in the range of 1.5 to 4. The energy of rupture, i.e. the area under the stressstrain curve from zero stretch to break, is high, above about 800 dyne cm. for 1 cm. of 3 denier filament. These filamentary materials are characterized by radial uniformity. They have a slightly pebbled surface. The products, when completely saponified, show relatively high overall birefringence above about 0.031, typical values being in the range of about 0.034 to 0.037. The filaments exhibit definite rubbery properties at elevated temperatures, eg about 220 C. They can be heat treated like other cellulose triacetate filaments to raise the safe ironing temperature and to improve the dimensional stability, resistance to creasing, permanence of the pleating, and the like. contrasted with other cellulose triacetates the material produced according to the Riley process shows substantially no shrinkage or decrease of tenacity on such heat treatment. In fact, the tenacity may even increase. For example, a filament having an original tenacity of 2.15 grams per denier when heat treated in air at 210 cycled between 217 C. and 223 C.

C. for 5 minutes shrinks less: tenacity of 2.37 grams per denie acetate filamentary material is also c sistance to creep at elevated temperature' with dry spun cellulose triacetate.

The rubbery properties of the products are de". strated in the following manner: A 125 denier 40 filament yarn is held at constant length (e.g. 10 inches) and heated to a temperature of 220 C. at a just perceptible initial tension (about 0.039 gram). The temperature is then It will be found that the tension on the filament increases as the temperature increases and decreases very perceptibly as the temperature decreases, typical of a rubber. By way of comparison, if the temperature of the filament is cycled between 162 C. and 168 C., the tension will be found to decrease as the temperature increases, typical of a glass.

The resistance to creep of the product is demonstrated as follows: One end of a filament is anchored within a horizontal heating tube. 10 inches from the anchored end, the filament is knotted to a glass filament which extends outside the tube and runs over a pulley. A weight is suspended from the protruding end of the glass filament. With various size weights suspended from the glass filament the tube is heated and the displacement of the weight with change in temperature is noted. Cellulose triacetate filaments produced by dry spinning the initial solutions begin to creep at about 168 C. The Riley filamentary materials do not creep comparably below about l78183 C. The rate and amount of creep for dry-spun filaments under a load of 0.033 gram per denier are only reached for the Riley filamentary materials at a load equal to or in excess of 0.067 gram per denier.

In accordance with the present invention there is provided a modified procedure for producing a product improved in certain respects. Specifically, the spin bath employed for coagulation of the dope contains up to about 20% and preferably about 5 to 12% by weight :of water. Beyond 20% of water spinning is unstable and the physical properties suffer. The methylene chloride concenrtration, C, which gives the most rapid stable spinning without interruption is approximately governed by the equation-C: T:50.8 water concentration. Thus, at a given temperature the concentration of methylene c1110- ride plus four fifths of the water concentration is approximately constant, i.e. as the water content is increased the methylene chloride content is decreased by four fifths the amount. That water replaces methylene chloride in the spin bath is quite surprising since water is a non-solvent for cellulose triacetate whereas methylene chloride is a solvent therefor. In practice, as the number of filaments being spun goes up the methylene chloride concentration of the spin bath should be decreased slightly due to the greater difficulty of the spin bath to penetrate to the core of the bundle of filaments, which core accordingly will exhibit a higher local methylene chloride concentration.

The use of water in the spin bath decreases thecoalescene between adjacent filaments which sometimes occurs when spinning into non-aqueous methylene chloride-methanol. In addition, the filaments produced in accordance with the present invention have a greater luster. They have less functionally effective crystallinity than filaments spun at the same temperature into nonaqueous spin baths (although higher spinning temperatures increase the crystallinity) and more orientation of the 'crystallites. This is evidenced by a decrease in the temperature at which the birefringence is zero, i.e. about 62 C. for the present invention for a material spun into a bath having almost 12% water at 32 C. as contrasted with 72 C. for a material spun into a non-aqueous spin bath. The decrease of crystallinity is further evidenced n 0.60. The the formation ting at and nts is unimpaired ightly at the higher [gives rise to procedural ne of the methylene chloride by water reducer ,umption of methylene chloride. In addition, the o. 16 of filaments, e.g tow, leaving the spinning column is less swollen and thus carries out less spin bath. This gives rise to the dual advantage that less solvent is lost because of the lesser amount of carried over liquid and the need for less heat to dry the tow.

As employed herein cellulose triacetate has reference to products having an acetyl value, calculated as combined acetic acid, preferably above 61% although Table 1 Bath Composition, Percent Tenacity, ElongagJd. tion, 1 0 OH Clz (II-1 0E Percent EXAMPLE II A 22.3% solution of cellulose triacetate, acetyl value 61.3%, in 91/9 methylene chloride/methanol is extruded through a spinnerette having 1396 holes of 100 micron diameter into a spinning column supplied with 6 liters per minute of various spin baths. The filaments are withdrawn from the spinning column at 8 0 meters per minute and are about 3 denier each. The spiunerette is positioned in a six inch inner diameter spin pot, 2 inches below a 1 inch high annular guide leading into a 55 inch long spinning column of 1 inch inner diameter; there is a tapered restriction extending over the lowermost 5 inches of the column and having a minimum passageway of /2 inch diameter. From the top of the column the tow passes a wiper guide to remove excess liquid, passes over a tensiometer pulley which places a predetermined tension on the filaments, passes about an idler roll and is pulled along by take-up rolls which feed it to a drier. The

results are summarized in Table II.

Table II Spin Bath Percent Spinning Tenac- Elon- Liquid Run Composition. Percent Tension, y. gation. on Tow Temp. mgJfii. g./d. Percent at Feed 0. R011 H2O CHzClz 0113011 acetyl values of 60% or slightly lower are permissible. The cellulose triacetate is dissolved in methylene chloride alone or in admixture with a small amount of a lower aliphatic alcohol such as isopropanol, ethanol or preferably methanol in up to about 15% by weight of the solvent mixture. As for the concentration of cellulose triacetate in the spinning solution, excellent results have been obtained within the range of 18 to 26%, about 20 to 23% being preferred.

The following examples are given to illustrate this invention further. All parts are by weight unless otherwise specified.

EXAMPLE I A 21.8% solution of cellulose triacetate, having an acetyl value of 6 1.5% calculated as combined acetic acid in 91/9 methylene chloride/methanol is extruded through a spinnerette having orifices each 100 microns in diameter into a one meter horizontal spin bath and is withdrawn at a speed of 75 meters per minute to produce a 120 denier tow. The spin bath temperature is 35 C. Tenacity and elongation, averages of ten single-fiber breaks on the Instron tester with a 1 inch gauge length and a strain rate of 60% per minute, are plotted against methylene chloride concentration for baths having 0.5, 9.4, 15.3 and 19.2% water. both tenacity and elongation are at a maximum at about the same methylene chloride concentration. The optima in the several runs are summarized in Table I.

An any given water content,

Comparing Runs 4 and 5 it will be seen that increasing the tension on the filaments generally produces an increase in tenacity at the expense of elongation.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention What We desire to secure by Letters Patent is:

1. Process for the production of cellulose triacetate filaments which comprises extruding in filamentary fiorm a solution of cellulose triacetate in a solvent therefor consisting essentially of methylene chloride and a lower aliphatic alcohol, said alcohol comprising up to about 15% by weight of said solvent, into a spin bath comprising a mixture of about 25 to 65 by weight of methylene chloride, a lower aliphatic alcohol and about 5 to 20% by weight of water.

2. Process as set forth in claim 1 wherein said spin bath is at a temperature of about 15 to 45 C.

3. Process as set forth in claim 1 in which the concentration of methylene chloride is at least about by weight in said solvent and at most about 65% by weight in said spin bath.

4. Process as set forth in claim 1 in which said alcohol is methanol.

5. Process as set forth in claim 4 in which said cellulose triacetate is dissolved in a solvent therefor comprising methylene chloride and a minor amount of methanol.

6. Process as set forth in claim 5, wherein the concentration of methylene chloride in said spin bath approximately equals 75 ATi5-0.8 Water concentration, Where T is the temperature of, the spin bath in C.

7. Process as set forth in claim 6, wherein the concentration of water in said spin bath ranges from about 5 to 12% by Weight.

8. Process for the production of cellulose triacetate filaments which comprises extruding in filamentary form a solution of cellulose triacetate in a solvent therefor comprising methylene chloride into a spin bath comprising a mixture of methylene chloride, methanol and about 5 to 20% by weight of Water, the methylene chloride concentration being approximately equal to 75% Ti50.8 water concentration, Where T is the temperature of the spin bath in C. and ranges from about 15 to 45 C.

9. Process as set forth in claim 8, wherein the concentration of Water in said spin bath ranges from about 5 to 12% by weight.

10. A cellulose triacetate filament exhibiting a tenacity of at least 1.8 grams per denier, an elongation of at least 18%, an energy ofi rupture equivalent to more than about 800 dyne cm. for a 1 cm. specimen of 3 denier filament, radial uniformity, an overall birefringence above about 0.031 when completely saponified, rubbery properties at 220 C., resistance to creep at 168 C., substantially no shrinkage on heat treatment, a pebbled surface, and an absence of X-ray diffraction maxima at 2 0 angles of 10 and 12.5

References Cited in the file of this patent UNITED STATES PATENTS 2,036,860 Dreyfus Apr. 7, 1936 2,143,205 Muller Jan. 10, 1939 2,145,076 Ehrenstein Jan. 24, 1939 2,768,870 Drisch Oct. 30, 1956 

10. A CELLULOSE TRIACETATE FILAMENT EXHIBITING A TENACITY OF AT LEAST 1.8 GRAMS PER DENIER, AN ELONGATION OF AT LEAST 18%, AN ENERGY OF RUPTURE EQUIVALENT TO MORE THAN ABOUT 800 DYNE CM. FOR A 1 CM. SPECIMEN OF 3 DENIER FILAMENT, RADIAL UNIFORMITY, AN OVERALL BIREFRINGENCE ABOVE ABOUT 0.031 WHEN COMPLETELY SAPONIFIED, RUBBERY PROPERTIES AT 220*C., RESISTANCE TO CREEP AT 168*C., SUBSTANTIALLY NO SHRINKAGE ON HEAT TREATMENT, A PEBBLED SURFACE, AND AN ABSENCE OF X-RAY DIFFRACTION MAXIMA AT 2 $ ANGLES OF 10* AND 12.5*. 